Greg Egan - The Arrows of Time

‘If it’s a choice between that and the destruction of the Peerless ,’ Ramiro replied, ‘then I don’t believe they’d choose the latter. Whatever their flaws, they’re not that deranged.’

Azelio was taking no comfort from the theory. ‘But are they deranged enough to think that that’s their choice? If you can’t avoid a meteor by choosing your trajectory, how can you avoid it just by switching off the messaging system?’

Agata had a different objection. ‘If they did shut down the system, wouldn’t that be an unsupported loop? They’d only be doing it because they learnt that it was going to happen.’

‘There’s not much complexity to it, though,’ Ramiro argued. ‘It’s hardly the same as learning a whole new theory of the vacuum from your future self; all they have to do is flick a switch.’

‘The Council wouldn’t want the mountain destroyed,’ Tarquinia agreed, ‘but they might well share Azelio’s view about their choices. They’ve come into this looking for a vindication of the system – so I don’t see anything inconsistent if they find themselves receiving three years’ worth of reports from the future that all describe them clinging to their original position: that the whole thing’s a boon, and there couldn’t possibly be any reason to shut it down deliberately.’

Ramiro ran his hands over his face. ‘Forget the Council, then. Let’s assume that there’s no chance of them causing the disruption. What’s the next most benign explanation?’

‘We could do it ourselves,’ Tarquinia suggested.

‘How?’ Azelio demanded. ‘What could we do that would be harder to see coming than a meteor at infinite speed?’

‘I have no idea yet,’ Tarquinia admitted. ‘But at least we’re isolated from the messaging system for a few more stints. We ought to be less vulnerable to the innovation block.’

Agata said, ‘But in the end, it would only be the shutdown itself that would have driven us to find a way to cause the shutdown.’

‘And that’s meant to stop us?’ Tarquinia was undeterred. ‘If that kind of loop really is too unlikely to be true, then we’ll find out eventually. But the only way to know is to try it.’

Ramiro recalled his own farcical attempt to steal the authorship of the fake inscription from her. It still seemed wisest to keep that to himself, but he didn’t need to confess anything to make the case for a more robust strategy.

He said, ‘There are plenty of people on the Peerless who could have planned this shutdown long before they heard about it.’

‘You mean saboteurs?’ Agata asked coldly. ‘The people who murdered the camera team? You want to replace a meteor strike with a bomb?’

‘Of course not.’ Ramiro spoke more carefully. ‘Most of the anti-messagers found those murders abhorrent, but a group of them could still be planning a way to cause the disruption without hurting anyone. And if they’re intent on using explosives at all, we can try to replace that with something better.’

Tarquinia understood. ‘We have seven stints to work out a plan of our own, and then we can try to sell it to these would-be saboteurs. That way it becomes a hybrid effort: their motives predate the news of the disruption, but if they’ve left the details too late we might be able to offer them a technological edge.’

Azelio hummed with frustration. ‘What’s all this talk of replacement? If a meteor is going to hit us, it’s going to hit us! You can devise as many ingenious plans as you like to try to sabotage the system at the very same moment, but if there’s a rock on its way, nothing you do is going to make it disappear.’

‘ If there’s a rock on its way, that’s true,’ Ramiro conceded. ‘But until we know that there is, why should we assume that? The history of the next twelve stints ends with the messaging system failing; we’re about as certain of that as we can be. Some sequence of events has to fill the gap between that certainty and all the other things we know. So which snippets would you rather the cosmos had on hand to complete the story? Just one, where a meteor hits the Peerless ? Just two: a meteor, or a bomb? Making our own preferred version possible won’t rule out everything else – but if we don’t even try, we’ll rule out our own best hope entirely.’

Agata brought a schematic onto her chest. ‘Whatever the details of the final design they used, each channel must have components something like this.’

Ramiro hadn’t thought about the technical aspects of the system for years, and as he reacquainted himself he was surprised by its apparent fragility. ‘Disrupt the light for a flicker, and the flow of information is cut. There’s no need to damage anything.’ Although the messages were constantly being converted into a less transient form to be boosted and re-sent, that version of the data only endured forwards in time – it couldn’t bridge a gap into the past. He’d often pictured the messages as a storehouse of documents, a kind of future-archeological find, but they were much more vulnerable than anything written on paper, or even in the energy states of a memory chip.

‘Could we launch some small objects into the external light paths?’ Tarquinia wondered. ‘If each one starts on the mountain close to one of the channel’s outlets, it could probably occult the target star without being picked up by a surveillance camera first.’

Azelio said, ‘The outlets will have to be on the base of the mountain, won’t they?’

‘Yes,’ Tarquinia replied. ‘Unless they’ve turned everything around while we were gone.’

‘We’d need to know exactly which orthogonal stars they’re using,’ Agata pointed out.

‘Maybe our collaborators will have that information already,’ Ramiro suggested. ‘So if we can offer them some miniature automated craft to fly up from the mountain and block those stars, why wouldn’t they use them?’

Azelio said, ‘So who’s going to build these things without being noticed? They’ll need accelerometers and photonics in order to navigate with any precision. If we make them ourselves on the Surveyor , we won’t stand a chance of smuggling them out when we dock. But on the Peerless , all the workshops and stores will be under surveillance.’

‘We could release them before we dock,’ Agata suggested. ‘Send them out to hide somewhere. If they’re small enough, and we time the whole thing carefully, they could pass from the Surveyor to the slopes undetected.’

‘And then what?’ Azelio pressed her. ‘They adhere to the slopes somehow, and then crawl towards the base – like insects crawling along a ceiling?’

‘Yes.’ Agata wasn’t backing down, but the proposal was growing more ambitious by the moment.

‘And then later,’ Azelio said, ‘since we won’t know the coordinates in advance, we have to be able to instruct them, remotely, to crawl to a particular take-off point and then fly along a certain trajectory. Without the signal being detected.’

Tarquinia disagreed with his last claim. ‘If a brief encrypted signal is picked up by the authorities, what can they do about it? So long as they can’t pin down the exact source or destination, mere detection need not be a problem. Even if they take it as a sign that some form of attempted sabotage is under way… they would have had that possibility in mind for the last three years, regardless.’

Azelio hesitated. ‘So why would they even try to stop us? They know the disruption is going to happen – so unless all this clandestine activity is irrelevant and a meteor is going to be responsible, this is a battle they know they can’t win.’